Location of valve for pressure gauge with ring syphon on a steam line 1

[mrev23]

Why place the valve between the syphon and the pressure gauge as shown in Figure 5 on page 7 of the following link?

http://www.spiraxsarco.com/pdfs/IM/p027_02.pdf

An arrangement with the valve between the pipe and the syphon (about 3/4 down the page, third image from the bottom, in the link below) seems safer to me.

http://www.instrumentationtoolbox.com/2013/02/an-introduction-to-pressure-gauges.html

I would omit the drain valve in the second link for my application.

Why place the shut-off valve at the end of a relatively flimsy tube? Why not place it on the pipe-side of the syphon, as in the second link? This would allow replacing the syphon without shutting down the main.

The valve location at the top of the syphon puts it outside the pipe insulation, but a nipple between the pipe and the valve would do that with material that is less vulnerable to damage.

Thanks. W.

 

[Drazen]

that's really a matter of your preferences.

if you put shutoff valve on top of the syphon, you can detach pressure gauge for calibration. saving some space is not negligible issue if pipes are run in tight space as height of this setup will define level of piping.

 

[ChasBean1]

I've never thought too much about this (until now) but think I like your philosophy of having isolability closer to mains and not at the end of frilly take-offs such as this. The U syphon or ring syphon is a potential point of failure (nobody ever steps on steam piping to access things above, right?). Yes, isolation capability closer to the main is better.

Good question and good post! CB

 

[danw2]

The Oil and Gas people with flammables in the pipe put either a root valve or an isolation valve with its fittings right on the pipe.

Here's typical company standard:

 

[RossABQ]

Note that many company's internal safety policies won't allow working on live systems without TWO isolation valves from the pressure source. Valves are (generally) cheap.